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My skyscraper is bigger: A case for building up, not out.

Besides making cities more affordable and architecturally interesting, tall buildings are greener than sprawl, and they foster social capital and creativity. Yet some urban planners and preservationists seem to have a misplaced fear of heights that yields damaging restrictions on how tall a building can be. From New York to Paris to Mumbai, there’s a powerful case for building up, not out.

…Again, the basic economics of housing prices are pretty simple—supply and demand. New York and Mumbai and London all face increasing demand for their housing, but how that demand affects prices depends on supply. Building enough homes eases the impact of rising demand and makes cities more affordable. That’s the lesson of both Houston today and New York in the 1920s. In the post-war boom years between 1955 and 1964, Manhattan issued permits for an average of more than 11,000 new housing units each year. Between 1980 and ’99, when the city’s prices were soaring, Manhattan approved an average of 3,100 new units per year. Fewer new homes meant higher prices; between 1970 and 2000, the median price of a Manhattan housing unit increased by 284 percent in constant dollars.

The other key factor in housing economics is the cost of building a home. The cheapest way to deliver new housing is in the form of mass-produced two-story homes, which typically cost only about $84 a square foot to erect. That low cost explains why Atlanta and Dallas and Houston are able to supply so much new housing at low prices, and why so many Americans have ended up buying affordable homes in those places.

Building up is more costly, especially when elevators start getting involved. And erecting a skyscraper in New York City involves additional costs (site preparation, legal fees, a fancy architect) that can push the price even higher. But many of these are fixed costs that don’t increase with the height of the building. In fact, once you’ve reached the seventh floor or so, building up has its own economic logic, since those fixed costs can be spread over more apartments. Just as the cost of a big factory can be covered by a sufficiently large production run, the cost of site preparation and a hotshot architect can be covered by building up. The actual marginal cost of adding an extra square foot of living space at the top of a skyscraper in New York is typically less than $400. Prices do rise substantially in ultra-tall buildings—say, over 50 stories—but for ordinary skyscrapers, it doesn’t cost more than $500,000 to put up a nice 1,200-square-foot apartment. The land costs something, but in a 40-story building with one 1,200-square-foot unit per floor, each unit is using only 30 square feet of Manhattan—less than a thousandth of an acre. At those heights, the land costs become pretty small. If there were no restrictions on new construction, then prices would eventually come down to somewhere near construction costs, about $500,000 for a new apartment. That’s a lot more than the $210,000 that it costs to put up a 2,500-square-foot house in Houston—but a lot less than the $1 million or more that such an apartment often costs in Manhattan.